This invention relates to compositions useful as tape joint sealing materials for installation of wallboard paneling. In particular, the invention relates to tape joint compounds which have an improved resistance to cracking during drying.
For many years, wallboard has been a standard material used to erect interior walls in the construction of buildings. Wallboard is typically installed in large panels that are nailed and glued to wall studs and fitted together until the wall section is covered. The joints where sections of board are butted together are covered with tape and the tape joints and all the nails are covered with a joint cement or tape joint compound. Upon hardening, the tape joint compound is sanded smooth so that it is imperceptible under paint or other wall covering.
Tape joint compounds typically comprise limestone, clay, mica, a binder, a thickener, and a stabilizer as the primary dry ingredients. Water is also the primary wet ingredient and may either be added to the dry ingredients by a manufacturer to form a ready-to-use mixture or added to the dry ingredients just prior to use by the actual user. In either ease, the tape joint compound will generally be a viscous, but workable, mass that is applied to a wall by troweling or other well-known methods.
The water demand to obtain a tape joint composition with the desired consistency will vary based upon several factors, including the viscosity of the thickener. In general, the water demand increases as the thickener viscosity increases. As more water is added to the formulation, its propensity to crack upon drying is increased. U.S. Pat. No. 4,558,079 discusses the tendency of water-soluble polymers used as thickeners, such as methylhydroxypropylcellulose (MHPC) and hydroxyethylcellulose (HEC), to adsorb to the surface of the clay used in the formulation, which can lead to mild flocculation. The flocculated particles leave crevices or voids which result in cracks when the compound drys. As such, it would be desirable to reduce the propensity of a tape joint compound to crack upon drying.
To aid in avoiding cracking and shrinkage of an aqueous adhesive for wall board compound upon drying, while maintaining a proper viscosity, U.S. Pat. 5,102,462 discloses the inclusion of a 3-n-butoxy-2-hydroxypropyl hydrophobically-modified hydroxy-cellulose with a crosslinked polyacrylic acid at a pH of 7 to 10. U.S. Pat. No. 4,558,079 discloses tape joint cement compositions which contain 0.2 to 2.0 percent by weight based on dry ingredients, of at least one hydroxypropylhydroxyethylcellulose having a hydroxyethyl substitution of 0.5 to 4.0 molecular substitution (M.S.) and a hydroxypropyl substitution greater than 0.36 to about 1.5 M.S. as a water retention aid and thickener. These cellulose derivatives were reported to have less of a tendency to adsorb to the surface of clays, particularly attapuligite, than either hydroxyethylcellulose or methylethylcellulose.
Despite what is known concerning joint compound formulations, there remains a need for improved tape joint compositions which have a reduced propensity for cracking upon drying and yet maintain the proper viscosity and workability for application to wall joints.